Archive for category Classification
Maximum Parsimony on a large data set of galaxies
Posted by astroclad in Classification, Diversity on August 1, 2019
Maximum Parsimony is known to be NP-complete and thus cannot really be used for a number of taxa larger than, say, 1000. Since the beginning of astrocladistics I was concerned by this problem, and it took us several years to find a solution. Indeed, we must cluster the data first, that is make a similarity […]
Multivariate Approaches to Classification in Extragalactic Astronomy
Posted by astroclad in Classification, General on December 18, 2015
This the title of our paper that makes a review of the tentative to base a (unsupervised) classification of galaxies on learning machine techniques : Multivariate Approaches to Classification in Extragalactic Astronomy Didier Fraix-Burnet, Marc Thuillard, Asis Kumar Chattopadhyay Frontiers in Astronomy and Space Sciences, 2015, 2 (3) It is an Open Access publication (not […]
Why?
Posted by astroclad in Classification, Complexity, General on March 30, 2015
Why multivariate analyses are not more widespread in astrophysics, especially in the extragalactic domain? I have not really the answer (I have some ideas though…), but let me show some plots that should help convince (astro)physicists. Firstly, do you remember this conference help in 1990? This shows that the debate about the morphological classification of […]
Transforming the Hubble Tuning Fork into a Piano
Posted by astroclad in Classification, General on February 4, 2015
A Tuning Fork is a device used to tune musical instruments. It vibrates at a single frequency, it is a pure sound of a single note. The Hubble Diagram not only looks like a Tuning Fork, but is also sounds like it: morphology is a single note, a single parameter, and it is based on […]
Gamma Ray Bursts and Cladistics
Posted by astroclad in Classification, General on July 25, 2013
Another kind of astronomical objects has been successfully analyzed with maximum parsimony: Gamma Ray Bursts! These are still mysterious objects, extremely violent, that emit a lot of gamma-rays during tenths of a second to several seconds. Gamma-rays are very energetic electromagnetic radiation, more so than X-rays, UV and of course visible light. Gamma-ray detectors on […]
When observations do not fit into tradition
Posted by astroclad in Classification on October 1, 2012
I have mentioned several times that the Hubble classification is a traditional approach of classification that is not adapted to modern data. I have also noticed that in the astrophysical literature modern statistical tools of clustering are often used in the sole purpose of retrieving the Hubble sequence without using the eyes. Or course, this […]
Evolutionary cost
Posted by astroclad in Classification on January 31, 2012
Cladistics looks for the relationships between taxa in terms of an evolutionary cost. By minimizing this cost, it is expected to find an evolutionary scenario that closely matches the hierarchical diversification process through transmission with modification. In other words, inheritance of innovations from common ancestors is the simplest way to explain diversity. To understand why […]
Cladistics and the Hubble sequence
Posted by astroclad in Classification on September 21, 2011
Hubble discovered galaxies in 1922. He found elliptically shaped objects and disky ones showing spiral arms sometimes with a bar at the center. He also thought that because of Jean’s law, elliptical galaxies would flatten into a disk, so the elliptical galaxies are the most ancestral ones. We can code Hubble’s initial observation with to […]
Opposite walks
Posted by astroclad in Classification, Diversity on August 10, 2011
Biologists have been confronted, right at the beginning (2000 years ago or so) , to the diversity of the living organisms on Earth. They had to do statistics and classification (systematics). Thanks to the progress of technology, they are now able to investigate the very detailed functioning of cells and molecules, asking physicists and chemists […]
Astrocladistics 